The present disclosure relates to methods, tools and systems for adjusting an external fixation frame. More particularly, the present disclosure relates to methods tools and system for repositioning the components of an external fixation frame according to a correction plan.
The external fixation market can be divided into two major segments: acute trauma and reconstructive. The customers, products, and needs of each segment are distinctly different. The trauma segment is dominated by modular fixators. These frames are characterized by limited componentry and very rapid application. Consequently, they are known for being fairly simple products. Most of these frames are used for temporizing fixation and quite often are only on the patient for hours or days.
The reconstructive segment leans heavily toward ring fixation. Ring fixators, such as the well known Ilizarov frame, are very popular. Such frames are shown in U.S. Pat. Nos. 4,365,624; 4,615,338; 4,978,348; 5,702,389; and 5,971,984. Their use of a combination of pins and wires to achieve a variety of polyaxial pin/wire attachments provides stability. They can accomplish a full six degrees of freedom and, when applied and managed well, can correct primary deformities while not creating secondary deformities. Rotational deformities are the sole domain of the ring fixator. However, mastery of the techniques and the products themselves can be a long and daunting process that it is not attractive to many users.
It is often necessary to realign, reposition and/or securely hold two bone elements relative to one another. For example, in the practice of medicine, bone fragments and the like must sometimes be aligned or realigned and repositioned to restore boney continuity and skeletal function. At times, this may be accomplished by sudden maneuver, usually followed by skeletal stabilization with cast, plate and screws, intramedullary devices, or external skeletal fixators.
A bone fragment can be moved, in general, from its original position as in a nonunion or malunion or from its intended position as in congenital deformities along six separate movements or degrees of freedom, a combination of three orthogonal translational axes (e.g., typical “X,” “Y” and “Z” axes) and three orthogonal rotational axes (e.g., rotation about such typical “X,” “Y” and “Z” axes).
External fixation devices are attached to the boney skeleton with threaded and/or smooth pins and/or threaded and/or smooth and/or beaded wires. Such constructs are commonly referred to as orthopaedic external fixators or external skeletal fixators. External fixators may be utilized to treat acute fractures of the skeleton, soft tissue injuries, delayed union of the skeleton when bones are slow to heal, nonunion of the skeleton when bones have not healed, malunion whereby broken or fractures bones have healed in a malposition, congenital deformities whereby bones develop a malposition, and bone lengthening, widening, or twisting.
A circumferential external fixator system was disclosed by G. A. Ilizarov during the early 1950s. The Ilizarov system includes at least two rings or “halos” that encircle a patient's body member (e.g., a patient's leg), connecting rods extending between the two rings, transfixation pins that extend through the patient's boney structure, and connectors for connecting the transfixation pins to the rings. Use of the Ilizarov system to deal with angulation, translation and rotation is disclosed in “Basic Ilizarov Techniques,” Techniques in Orthopaedics®, Vol. 5, No. 4, December 1990, pp. 55-59.
Prior art orthopaedic external fixators differ in their ability to move or adjust one bone fragment with respect to the other in a gradual fashion. Some allow gradual translation, others allow gradual rotation about two axes. The Ilizarov system can provide an external fixation device that could provide gradual correction along and about six axes; however, such a device would require many parts and would be relatively complicated to build and use in a clinical situation.
Often orthopaedic external fixators such as Ilizarov fixators must be repositioned after their initial application. Such modification may be necessary to convert from one correctional axis to another or to convert from an initial adjustment type of fixator to a weight bearing type of fixator, some of the correctional configurations not being stable enough for weight bearing.
A “Steward platform” is a fully parallel mechanism used in flight and automotive simulators, robotic end-effectors, and other applications requiring spatial mechanisms with high structural stiffness and includes a base platform, a top platform, and six variable limbs extending between the base and top platforms. See S. V. Sreenivasan et al., “Closed-Form Direct Displacement Analysis of a 6-6 Stewart Platform,” Mech. Mach. Theory, Vol. 29, No. 6, pp. 855-864, 1994.
Taylor et al. U.S. Pat. No. 5,702,389, which entire disclosure is incorporated by reference herein, relates to a fixator that can be adjusted incrementally in six axes by changing strut lengths only, without requiring joints to be unclamped, etc. This patent includes a first ring member or swash plate for attachment relative to a first bone element; a second ring member or swash plate for attachment relative to a second bone element. Six adjustable length struts having first ends movably attached to the first member and second ends movably attached to the second member are provided. The first ends of the first and second struts are joined relative to one another so that movement of the first end of one of the first and second struts will cause a corresponding movement of the first end of the other strut, with the first ends of the third and fourth struts joined relative to one another so that movement of the first end of one of the third and fourth struts will cause a corresponding movement of the first end of the other strut. The third and fourth struts and fifth and sixth struts are similarly joined. Second ends of the first and sixth struts joined relative to one another so that movement of the second end of one of the first and sixth struts will cause a corresponding movement of the second end of the other strut. Second ends of the second and third struts and fourth and fifth struts are formed in a similar manner. Thus, changing the length of the struts effects reposition of the bone segments. The mathematics of this adjustment is set forth in the patent and may be programmed into a computer for use with the tool of the present invention.
As discussed above, most external fixators should be adjusted over a period of time to reposition bone segments. The adjustment of the external fixation may be implemented according to a “prescription” or correction plan. Physicians may adjust the external fixator at precise times over a period of time (e.g, on a daily basis for three weeks). Patients, however, may not desire to visit the physician's office every time an adjustment is needed. For this reason, many external fixators can be adjusted by the patients themselves without the assistance of a physician. The adjustment of the external fixator should nonetheless strictly comply with the predetermined correction plan. In some occasions, patients may not adjust their own external fixator according to the correction plan for a variety of reasons. For instance, patients may not understand how to use the external fixator correctly. In addition, when the patients themselves adjust the external fixators, physicians may not even know whether patients are in fact adjusting the external fixators according to the correction plan. For the foregoing reasons, it is desirable to provide a tool, system and/or method for helping a patient implement a correction plan in an external fixator.